How do I make weight painting not a living torment?
Retopologize your mesh. Once you´re done, then you can assign weights using armature.
Also: Select your mesh, use the modifier: DECIMATE: Choose 50%. Check if your model is ok for you in shape. If it is and you´ve reduced the polycount to half, please reconsider retopologize. Basically you can´t work with an armature on a very dense mesh.

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BFCT_Schiller